1. Field of the Invention
The present invention relates to a method of manufacturing a nozzle plate, a liquid ejection head, and an image forming apparatus including a liquid ejection head, and more particularly, to technology for forming a liquid-repelling film on the surface of a nozzle plate in which a plurality of very fine liquid ejection ports (nozzles) for ejecting liquid are formed, and to a liquid ejection head and an image forming apparatus using a nozzle plate.
2. Description of the Related Art
An inkjet printer (inkjet recording apparatus) is known as an image forming apparatus. The inkjet recording apparatus includes an inkjet head (liquid ejection head) where a plurality of nozzles (ejection ports) for ejecting ink (liquid) are arranged, and forms an image on a recording medium by ejecting ink from the nozzles while the inkjet head and the recording medium are caused to move relatively to each other.
Various methods are known as ink ejection methods for an inkjet recording apparatus. For example, a piezoelectric method is known, in which a diaphragm that constitutes a portion of the pressure chambers is deformed and the volume of the pressure chamber is changed by the deformation of a piezoelectric element. Thereby, ink is introduced into the pressure chamber from an ink supply passage when the volume of the pressure chamber is increased, whereas the ink inside the pressure chamber is ejected from the nozzles in the form of ink droplets when the volume of the pressure chambers is decreased.
In an inkjet recording apparatus of this kind, by forming a liquid-repelling film on the surface of the nozzle plate in which the nozzles of the ink ejection head are formed, soiling of the nozzles can be removed more readily, leakage of ink from the nozzles is reduced, and the direction and volume of ejection of the ink can be stabilized.
In order to form both nozzle apertures and a liquid-repelling film, broadly speaking, there is a method of forming a liquid-repelling film after forming nozzle holes in the nozzle plate, and a method of forming nozzle holes after forming a liquid-repelling film on one surface of the nozzle plate.
Of these methods, in the case of a method of forming the nozzle holes afterwards, the method for forming the holes is, in practice, limited to a method of laser processing of a heat resistant resin, such as polyimide, (using an excimer laser, for example), and hence there are restrictions on the types of device used to form the holes. Therefore, the method where the liquid-repelling film is formed after forming the nozzle holes is used more frequently, in general.
However, in the method of forming a liquid-repelling film afterwards, it is difficult to leave the liquid-repelling film in an orderly shape around the perimeter of each nozzle, and therefore various methods of manufacturing a nozzle plate have been proposed.
For example, Japanese Patent Application Publication No.7-304175 discloses a method for manufacturing a nozzle plate having a liquid-repelling film formed around the periphery of each nozzle. In this method, nozzles are formed in a substrate, and a liquid-repelling film is formed on the surface of a substrate surrounding the positions where the nozzles have been formed. Then, blast processing is carried out to cause minute solid particles to impact to the liquid-repelling film from the rear side of the surface of the substrate on which the liquid-repelling film is formed, thereby removing the unwanted portions of the liquid-repelling film. In this method, after blast processing, burring arises toward the side exterior to the nozzles, and this burr is heated to be softened and removed.
The method using the above-described blast process can lead to the enlargement of the nozzle diameter, deformation of the actual nozzle plate, roughening of the nozzle plate surface, and the like. In view of these, Japanese Patent Application Publication No. 2004-142297 discloses a method of manufacturing a nozzle plate in which nozzle holes are formed in a nozzle plate, a liquid-repelling film is formed on the surface of the nozzle plate, and the liquid-repelling film in the positions where the film blocks the nozzle holes up is removed according to a so-called water jet that water is sprayed onto the liquid-repelling film from the rear face of the plate.
However, if it is sought to remove unwanted portions of the liquid-repelling film formed on the surface of a nozzle plate by means of the blast process or water spray from the rear face of the nozzle plate, as described above, then there is a possibility of removing parts of the liquid-repelling film that do not need to be removed, and hence it is difficult to keep the accuracy of the nozzle plate.
Furthermore, since the film is removed by the impact of the blast material or water, the liquid-repelling film and the nozzle plate themselves may deform, or internal stresses may be generated therein.